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Abstract This study investigates the synergistic effect of ultrasonication and antimicrobial action of antimicrobial peptide cecropin P1 on the inactivation of Escherichia coli O157:H7 in a cylindrical ultrasonication system. The inactivation of E. coli at pH 7.4 was performed using: ultrasonication (14, 22, and 47 kHz), cecropin P1 (20 µg/mL), and a combination of both. We found the treatment at 22 kHz, 8W for 15 min of exposure and a combination of ultrasound at higher frequency (47 kHz, 8 W) and cecropin P1 for one minute of exposure were more efficient, reducing the cell density by six orders of magnitude, compared to individual treatments (ultrasound or cecropin P1 only). Dye leakage studies and transmission electron microscopy further validated these results. A continuous flow system was designed to demonstrate synergism of ultrasonication with antimicrobial peptide Cecropin P1 in the inactivation of E. coli; synergism was shown to be more at higher ultrasonication frequencies and power levels. Acoustic cavitation by ultrasonic treatment could drastically improve microbial deactivation by antimicrobial peptides cecropin P1 by increasing their ability for pore formation in cell membranes. A continuous ultrasonication and antimicrobial peptides system can lead to an energy-efficient and economical sterilization system for food safety applications.

Alamethicin (ALM) inhibits the growth of bacteria by disrupting their cell membrane. ALM exhibits poor solubility in aqueous medium thus limiting its application. A method is proposed for encapsulation of ALM with γ-cyclodextrin (γ-CD) by forming a complex of higher solubility with thermal and pH stability as confirmed by FT-IR and DSC, thus greatly improving its application in food safety. Molecular dynamics simulation suggested a stable configuration of the complex when hydrophobic residues are inserted into the hydrophobic cavity of γ-CD. Aggregation of the complex was inhibited at higher γ-CD/ALM molar ratio. γ-CD/ALM complex exhibited significant antimicrobial activity against L. monocytogenes with the minimum inhibitory concentration being dependent on γ-CD/ALM molar ratio (>0.429 mg/mL for 1:1; >1.094 mg/mL for 5:1; >2.078 mg/mL for 10:1). Optimum γ-CD/ALM molar ratio for maximum antimicrobial activity is the result of competing effects of higher solubility and shielding of hydrophobic ALM groups by γ-CD.

A molecular dynamics simulation of mixtures of 26-mer amylose with three different egg yolk lipids, namely, cholesterol, triglyceride and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), demonstrated the formation of a stable complex. The 26-mer amylose fluctuated between a coiled and an extended helical conformation. The complex was a V-type amylose complex, with the hydrophobic tail of the lipids being inside the hydrophobic helical cavity of the amylose. The number of glucose units per turn was six for the two helical regions of the amylose-POPC complex and the palmitoyl tail region of the amylose-triglyceride complex. This value was eight for the cholesterol and the two-tail helical region in the amylose-triglyceride complex. Two tails of the POPC were in two different hydrophobic helical regions of the 26-mer amylose, whereas the palmitoyl tail of the triglyceride lay in one hydrophobic helical region and the linoleoyl and oleoyl tails both lay in another helical region, and the cross-sectional area of the latter was larger than the former to accommodate the two tails. The radii of the gyration of the complex were lower for all three cases compared to that of one single amylose. In addition, the stability of the complexes was ranked in the following order: POPC < cholesterol < triglyceride, with their average binding energy being −97.83, −134.09, and −198.35 kJ/mol, respectively.

Emulsions can be prepared from protein microgel particles as an alternative to traditional emulsifiers. Prior experiments have indicated that smaller and more deformable microgels would decrease both the physical destabilization of emulsions and the diffusion-based losses of entrapped volatile molecules. The microgels were prepared from β-lactoglobulin with an average diameter of 150 nm, 231 nm, or 266 nm; large microgels were cross-linked to decrease their deformability. Dilute emulsions of 15–50 μm diameter were prepared with microgels by high shear mixing. Light scattering and microscopy showed that the emulsions prepared with larger, untreated microgels possessed a larger initial droplet size, but were resistant to droplet growth during storage or after acidification, increased ionic strength, and exposure to surfactants. The emulsions prepared with cross-linked microgels emulsions were the least resistant to flocculation, creaming, and shrinkage. All emulsion droplets shrank as limonene was lost during storage, and the inability of microgels to desorb caused droplets to become non-spherical. The microgels were not displaced by Tween 20 but were displaced by excess sodium dodecyl sulfate. Hexanol diffusion and associated shrinkage of pendant droplets was not prevented by any of the microgels, yet the rate of shrinkage was reduced with the largest microgels.

Nanoparticles possess unique properties as a result of their large surface area per unit volume and therefore can be functionalized by the immobilization of enzymes for a variety of biosensing applications. Changes in the tertiary conformation of -lactoglobulin adsorbed on 90 nm silica nanoparticles with time were inferred using tryptophan fluorescence and Fourier transform infrared spectroscopy (FTIR) for different surface concentrations, temperature, pH, ionic strength, and 2,2,2-trifluoroethanol (TFE) and dithiothreitol (DTT) concentrations. Rapid initial unfolding followed by a much slower rate at longer times was observed, with the extent of unfolding being higher at lower surface concentrations, higher ionic strengths, higher temperature, higher TFE and DTT concentrations, and pI. The effect of temperature on the unfolding of adsorbed protein on the nanoparticle surface was similar to that in the bulk even though the extent of unfolding was higher for adsorbed protein molecules. The results of the extent of change in tertiary conformation using FTIR as indicated by the change in the ratio of amide II‘/amide I were consistent with those obtained by tryptophan fluorescence whereas the rates of conformational changes given by FTIR were found to be much faster. Circular dichroism (CD) spectra showed that altering the surface concentration by itself did not change the secondary structure of -lactoglobulin on the surface. TFE was found to increase the helix content at the expense of the fraction of the sheet, whereas the sheet was converted to an unordered conformation in the presence of DTT. [ABSTRACT FROM AUTHOR]

A generalized formalism for the rupture of a draining foam film due to imposed random pressure fluctuations, modeled as a Gaussian white noise, is presented in which the flow inside the film is decomposed into a flow due to film drainage and a flow due to imposed perturbation. The evolution of the amplitude of perturbation is described by a stochastic differential equation. The rupture time distribution is calculated from the sample paths of perturbation amplitude as the time for this amplitude to equal one-half the film thickness and is calculated for different amplitudes of imposed perturbations, film thicknesses, electrostatic interactions, viscosities, and interfacial mobilities. The probability of film rupture is high for thicker films, especially at smaller times, as a result of faster growth of perturbations in a thick film due to a smaller disjoining pressure gradient. Larger viscosity, larger surface viscosity, higher Marangoni number, and smaller imposed pressure fluctuation result in slower growth of perturbation of a draining film, thus leading to larger rupture time. It is shown that a composite rupture time distribution combining short time simulation results with equilibrium distribution is a good approximation. [ABSTRACT FROM AUTHOR]